how to normalize the state space for articulated robot environments?
This paper might provide some answers https://arxiv.org/pdf/1810.05762.pdf

For the observations / states they used not only angles, but also velocities, heights and positions (Table 2).

In 4.2 Learning algorithm you can see that they mention this, which is related to your question about normalization:


  Additionally, for stability we whiten the current observations by
  maintaining online statistics of mean and standard deviation from the
  history of past observations.